One of the main tasks for biological research today is to decipher a whole system of biologically relevant information that exists on the cell surface. The regulation of the number and distribution of membrane components is one way in which this information is expressed. Two cell surface molecules whose number and distribution are highly regulated both in vivo and in vitro are the acetylcholine receptor (ACHR) and the acetylcholine esterase (ACHE). These molecules are particularly interesting to focus on: (a) They have been fairly extensively studied and good tools have already been developed for their study (alpha-Bungarotoxin for example), (b) They are essential components of the neuromuscular junction and their study promises a greater understanding of both the cell surface and cholinergic synapse, (c) These molecules are also useful for the study of various myogenic pathologies such as the muscular dystrophies. We will investigate various aspects of the regulation of ACHR and ACHE molecules on myotubes in cell culture. We will study aspects of ACHR stability and mobility on the myotube surface in cell culture. We will study the mechanism by which different agents either induce or repress ACHR and ACHE. We will investigate the direct effects of spinal cord explants on ACHE isozyme patterns and we will continue our efforts to purify ACHR enriched membrane vesicles from freshly dissociated myoblasts and myotubes grown in cell culture.